This invention relates to a fuel control or metering valve for fuel injection apparatus for a mixture compressing spark ignition internal combustion engine provided with continuous injection. In particular the invention is concerned with a valve having a piston rotatable in a cylinder to control the throttle cross-section of a port in the cylinder wall.
With a fuel metering valve of the type mentioned (known e.g. from German Specification 1934703), which is intended to permit accurate metering of fuel according to the internal combustion engine's operating conditions at any particular time, the throttle cross-section, which is variable for this purpose, is obtained, through rotation of the control piston relative to the control cylinder, by virtue of the fact that an oblique control edge on the control piston is moved across a rectangular port in the control cylinder, when the control piston rotates, as a function of the amount of air flowing through the induction manifold of the engine, the throttle cross-section changes in accordance with a sine curve. The result of this is that during rotation of the control piston between the smallest and largest throttle cross-sections an amount of fuel is metered each time, which, starting from the smallest throttle cross-section, initially increases more rapidly and, after about half the control piston's movement, increases more slowly. Such a metering pattern does not correspond to the amount of fuel required in all operating ranges. For example, the decrease or levelling-out in the increments of fuel dosage from halfway along the control piston's path--i.e. from half load to full load--results in a relative reduction in the amount of fuel in this operating range and thus in a thinning of the mixture fed to the internal combustion engine. A further disadvantage with the type of valve mentioned consists in the fact that it is only possible to provide one single port to interact with the control edge on the piston through which the fuel is metered even when several injection nozzles are used. If an injection nozzle becomes blocked in such an arrangement, the amount of fuel normally discharged through this injection nozzle will be transferred to the remaining injection nozzles, and this results in an increase in the proportions of noxious substances in the exhaust gas.